Miley posted a message saying: "Before Amanda Bynes... There was..." alongside a screengrab of a string of Sinead's old tweets. One reads: "Does any1 know a psychiatrist in dublin or wicklow who could urgently see me today please? im really un-well... and in danger (sic)."

In response, the Irish songstress wrote a furious reply to the Wrecking Ball singer threatening to sue: "You have posted today tweets of mine which are two years old, which were posted by me when I was unwell and seeking help so as to make them look like they are recent. In dong so you mock myself and Amanda Bynes for having suffered with mental health issues and for having sought help.

"Remove your tweets immediately or you will hear from my lawyers. I am certain you will be hearing from all manner of mental health advocacy groups also. It is not acceptable to mock any person for having suffered."

Now the 20-year-old twerk queen has responded on Twitter, saying: "Sinead. I don't have time to write you an open letter cause I'm hosting & performing on SNL this week.

"So if you'd like to meet up and talk lemme know in your next letter. :)"

In it, she says: "I am extremely concerned for you that those around you have led you to believe, or encouraged you in your own belief, that it is in any way ‘cool’ to be naked and licking sledgehammers in your videos.

"It is in fact the case that you will obscure your talent by allowing yourself to be pimped, whether it’s the music business or yourself doing the pimping."

"The music business doesn’t give a s**t about you, or any of us.

"They will prostitute you for all you are worth, and cleverly make you think its what YOU wanted and when you end up in rehab as a result of being prostituted, ‘they’ will be sunning themselves on their yachts in Antigua, which they bought by selling your body and you will find yourself very alone."

Miley’s Wrecking Ball video, which sees her straddling a concrete ball naked and licking a hammer, was slammed as porn by critics, whereas Nothing Compared To U, directed by John Maybury and written by Prince in 1990, picked up MTV Award for Video of the Year.

As well as warning Miley to be self-aware, Sinead praises her talent and urges her to just focus on the music.

"As for the shedding of the Hannah Montana image, whoever is telling you getting naked is the way to do that does absolutely NOT respect your talent, or you as a young lady," she wrote.

"Your records are good enough for you not to need any shedding of Hannah Montana.

"She’s waaaaaaay gone by now.. Not because you got naked but because you make great records."